Amphidiploid Dwarf and Median Bearded Irises

Iris 'Gizmo'When I. pumila is crossed with a 48-chromosome bearded iris (such as a modern tall bearded), the result is a plant with two sets of 8 chromosomes from I. pumila and two sets of 12 chromosomes from the other parent. This configuration (known as an amphidiploid) is generally fully fertile. The modern standard dwarf bearded irises virtually all belong to this 40-chromosome fertile family. Amongst wild irises, the species I. lutescens in its various forms has essentially the same chromosome makeup, and is thus also part of the same fertile family. Other apparent members of this family are I. bicapitata and I. subbiflora.
I. sp. aff. reichenbachii ex Vardar Gorge probably belongs in this group as well.

Many fine new SDBs are produced each year, so this family is going strong, second only to the tall beardeds in the popularity and attention it receives.

The family can be expanded by making new pumila x 48-chromosome bearded iris crosses. The original crosses that launched the SDBs involved a number of forms of I. pumila along with a range of TBs from the mid-20th century. It might be valuable to use different, modern TBs and BBs as parents, and to use the 48-chromosome medians as well. If the TBs are used, the seedlings will likely be larger than ideal for SDBs, but if the medians are used, they are likely to be smaller, even falling in the MDB range. Ben Hager produced a number of nice MDBs via this route, and in fact many modern MDBs are of this sort, either derived from Hager's lines, or simply short selections from SDB breeding. Still, the potential here is not exhausted by any means.

I want to bring different species into the mix, and the primary reason for doing so is to improve the options for the MDB class.

In Hager's time (1960s through 1990s or so), most widely grown MDBs were the result of crossing SDBs with I. pumila. These had a very distinct character: early, very prolific bloom, with a daintiness instantly distinguishable from the SDBs. You may be familiar with old favorites of this type, such as 'Alpine Lake' and 'Zipper'. Unfortunately, most of these had very little fertility, being unbalanced tetraploids with three pumila sets and only one TB set. Hager thought that improvement in the MDB would only come if they were fertile and could be bred with one another for multiple generations, like the SDBs.

He had misgivings about just selecting small SDBs, however, skeptical that they could preserve the distinctive qualities of the MDBs. Interestingly, this is exactly where the hybridizing world has gone in recent decades. Almost all new MDBs introduced today are just small selections from SDB lines. People seem to like them and grow them (I do myself), but I know I'm not the only one who feels the line between MDBs and SDBs has blurred a little too much. Many of these modern ones are right at the top height limit of the class, not really distinguishable from SDBs without a ruler, and in some cases not particularly early blooming, which has been one of the attractions of the MDBs historically.

Hager's idea was to work within the 40-chromosome family, but to use other-than-TB types and species with I. pumila to ensure daintier flowers. In particular, he advocated I. aphylla and the aphylla-derived tetraploid MTBs. MDBs from this kind of breeding are fertile with one another, and also fertile with the SDBs, so the hope was that one could take advantage of advancements in SDBs for MDB breeding without losing either fertility or daintiness.

Hager had nice results from this approach, including favorites like 'Gizmo' and 'Libation', among quite a few others. But subsequent hybridizers largely left this project behind, in favor of the SDB-only approach, which gives more immediate results.

Now, however, we have some opportunities to revisit this program. The tetraploid MTBs have improved a great deal. Using them directly with Iris pumila to produce dainty MDBs seems promising, and is a largely unexplored area. Also, there are other even smaller tetraploid species that can be used in place of I. aphylla. I. schachtii is available now, as is I. junonia, and tetraploid forms of I. reichenbachii if one can find them. Any of these crossed with I. pumila should give small MDBs that are fully fertile with SDBs and their modern MDB offspring. 

There are also some 40-chromosome species of MDB or SDB size that have not been used significantly in modern SDB breeding, including Ii. lutescens, subbiflora, and bicapitata.

So I'm on my way to creating a mixing pot with these three ingredients:

1. Seedlings from I. pumila crossed with I. aphylla, tet MTBs (or small BBs), I. schachtii, I. reichenbachii, or I. junonia - for daintiness, early bloom, and "wildflower charm" for those who appreciate such things

2. SDBs and MDBs from SDB breeding - for refined form and substance and diverse color patterns

3. Ii. lutescens, subbiflora, bicapitata - just to learn if they have any valuable distinctiveness to contribute.

I don't expect a project like this to make any dent in the popularity of modern SDB-type MDBs, but it will be fun to see what can be done.

 

Hall of Fame

Greenspot (Paul Cook, R. 1951). Seedling 2148. SDB, Height 10" (25 cm), Early bloom season. White self green spot on falls. Cook 10942 X yellow I. pumila. Honorable Mention 1951, C-D '59, CDM 1968. Longfield 1951.

Although there are any number of those first-generation SDBs from the pioneering TB x I. pumila crosses that might be singled out as classic achievements, I have selected 'Greenspot' because of its enduring popularity as a garden plant and its use in many different types of breeding over the years. It showed off the potential of the pumila spot pattern in median breeding and modeled the flower and plant proportion desirable for the SDB class.

Lenna M (Earl Roberts, R. 1964). Sdlg. 64R13. SDB, 10" (25 cm), E. Color Class-OlP, S pink; F pink, deeper beige spot, white-pink border; white beard tipped red. (TB orchid sdlg. x Barium Gold) X Zickler sdlg: ((Twilight Sky x white pumila) x (Desert Song x white pumila)). Roberts 1966.

Early on in SDB breeding, it was thought that the recessive TB color patterns, such as the plicata pattern and the tangerine pinks, might not be possible in the SDB class. I have chosen 'Lenna M' as an example of an early breakthrough in this area; it was quite a sensation in its day as a pink SDB and was much used in breeding. Although it would be a number of years until pink and orange SDBs improved enough to win top awards, these early accomplishments laid the groundwork for the great color variety we have today.

Libation (Ben Hager, R. 1974). Seedling AHD2541B . MDB, height 5" (13 cm), Mid to Late bloom season. Standards wine red; falls deeper wine red, darker spot area; yellow beard. 'Prodigy' X ('Scale Model' x 'Brownett'). Melrose Gardens 1975. Caparne Award, 1979.

I've included 'Libation' as an early and popular example of Ben Hager's work in producing MDBs from combining I. pumila with his aphylla-based tetraploid MTB lines. MDBs from this type of breeding are fully fertile with SDBs, but retain a natural daintiness appropriate to the miniatures. It is partly because of such work that so many nicely formed and varied MDBs are available today.

Chubby Cheeks (Paul Black, R. 1984). Seedling 824E. SDB, height 12" (30 cm), Early bloom season. Standards white ground, stitched light violet, greyed chartreuse band; falls white ground, stitched violet around outer portion, widely banded greyed chartreuse; pale violet beard tipped tangerine in throat; ruffled; pronounced sweet fragrance. Sdlg. 824E:( Black's Seedling B80-20 : (Concord Touch x Daisy) X Soft Air). Mid-America Iris Gardens 1985. CDM 1991.

The wide-petaled form of this SDB has transformed the class. It is arguably the best SDB breeder ever produced, with a multitude of superior offspring introduced over a span of more than two decades.

 

Gallery

MDB 'Dollop of Cream'
(Black, 2006)
SDB 'Pussycat Pink'
(Black, 2006)
SDB 'Urban Myth'
(Chapman, 2010)
I. subbiflora S004-01
SDB 'Kaching'
(Black, 2009)
S006-01 (I. aphylla X I. pumila)

 Plant List

The list below shows the name of each plant I currently grow for breeding purposes, the source, and the year acquired.

Abuzz with Charm

Carol Coleman

2013, 2014

Bluebeard's Ghost

Mid-America Garden

2011

Dollop of Cream

Mid-America Garden

2011

Eye of the Tiger

Mid-America Garden

2013

Heart Stopper

Carol Coleman

2014

Kaching

Mid-America Garden

2012

Keeno

Mid-America Garden

2014

Icon

Mid-America Garden

2013

Pearly Whites

Mid-America Garden

2014

Riveting

Mid-America Garden

2014

I. sp. aff. reichenbachii ex Vardar Gorge

Iris Colorado

2011

chromosome configuration uncertain

Hildebrandt (SIGNA) 05B011: seedling of
I. sp. aff. reichenbachii ex Vardar Gorge

Hildebrandt's

2011

chromosome configuration uncertain

I. subbiflora S004-01

ex Spain, from SIGNA seed

S006-01

I. aphylla AA X I. pumila "clausii"

Illustration: 'Gizmo' (Hager '76): an MDB from I. aphylla breeding.

 

Tom Waters

September 2010

updated March 2017

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Unless otherwise noted, all text and illustrations copyright Tom Waters and all photographs copyright Tom or Karen Waters. Please do not reproduce without permission.